Quick update here. We started on the Magnesium and the leg cramps are gone. Not only that, but his energy level has increased exponentially and he has been running non stop. It shows just how much of an issue this has been for him. Thank you all for your help.
Glad it helped. I take Magnesium just before bed and first thing in the morning (400 mg total - sometimes 600mg) - you should too.
Also make sure your 4 yr. old has his vitamin D level tested. It needs to be in the 30-50 ng/ml range. Children (as well as parents) are often deficient in vitamin D because we keep the kids out of the sun.
Other minerals to be aware are zinc and selenium. Usually when one is magnesium deficient, we tend to be deficient in other minerals as well. A few Brazil nuts (and I mean a few, like only two) as well as beef and spinach will be good for selenium and zinc. No need for supplements for these unless he doesn't like meat (vegetarian) and doesn't like Popeye.
(The only good thing to come out of my CML disease is that I learned so much about nutrition and eat so much better than before the disease. It is the ONLY good thing about CML.)